Liquids in containers are not dimensionally stable but react to each container movement with a self-movement. Depending on the filling level of the container, this results in different physical effects which, depending on the movement pattern, can significantly influence the self-movement of the container, in particular in the case when the container itself is being maneuvered, thus is moving.
One such example is a tank of a vehicle (e.g., land vehicles, watercrafts, aircrafts or spacecrafts) filled with a fluid. When the vehicle carries out a rapid movement change, temporally delayed forces of the now moving fluid can be induced back into the vehicle, which forces, in turn, influence the movement of the vehicle itself. It is therefore often helpful and required to be able to foresee the behavior of the fluid in the container during certain movements or movement changes of the vehicle in order to be able, for example, to consider the reactions induced by the fluid on the vehicle when controlling the same.
A particular need for such predictions arises when dropping additional tanks or other loads provided with a liquid container such as, for example, cruise missiles, or motor vehicles airdropped from aircrafts. Also, dropping tanks from a starting rocket or from a spacecraft in space requires being able to predict the self-movement of the liquid still remaining in the tank.
Such predictions can avoid a path change of the dropped tank that results in a collision with the original carrier vehicle, for example, with the aircraft, due to the self-movement. Such predictions have to be carried out as simulations in order to obtain, for example, approvals for aircrafts or approvals for certain airdrop maneuvers. However, they have also to be carried out, for example, to simulate certain dropping procedures for an aircraft so that during the actual operation, no accidents occur such as collisions of the dropped object with the aircraft dropping said object.
It is also helpful to be able to carry out such simulations in adequate airborne computers in order to determine a safe dropping time in a corresponding dropping procedure and to technically allow the airdrop only at that time.
In order to be able to simulate the movement properties of the container partially filled with a fluid, the unsteady physical properties of the fluid in the container must be known. Simulating fluid movements in a container is traditionally carried out on the basis on equations of motion of frictionless and viscous flows. Other calculation approaches use very sophisticated interrelations on the basis of nuclear physics and molecular movements. These methods are very accurate in the appropriate formulation, however, for implementation, they need very large computing capacities in order to obtain a result. Such computing capacities are often not available aboard vehicles and even in the case of an external simulation on the ground, under certain circumstances, they can take several hours or even days.